Particle counter
Inventors
SAITOU, Mitsuaki • SHIMMURA, Masaki • Matsuda, Tomonobu • Yamakawa, Yuki
Assignees
Publication Number
US-10416069-B2
Publication Date
2019-09-17
Expiration Date
2038-11-26
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Abstract
A particle counter provided with: a detector configured to receive interference light by scattered light and reference light with a light receiving element, and generate a detection signal corresponding to the interference light; a filter configured to perform, with respect to the detection signal generated by the detector, a filtering process for passing a frequency component corresponding to an intensity change of the interference light; a determination unit configured to determine, from a peak level of the detection signal before filtering and a peak level of the detection signal after filtering, whether the detection signal is due to a particle; and a counting unit configured to perform, if it is determined by the determination unit that the detection signal is due to the particle, particle counting based on the detection signal after filtering.
Core Innovation
The invention discloses a particle counter that utilizes interference between scattered light from particles in a fluid and reference light to generate a detection signal indicative of particle presence. A light source emits coherent light which is branched into two paths: one for irradiating particles in a fluid in a detection area and one for reference light. A light superimposition unit causes interference of the scattered and reference lights, and a detector receives this interference light, generating a detection signal corresponding to it.
To improve measurement accuracy by reducing noise-related false particle counts, the invention provides a filter that passes frequency components corresponding to intensity changes of the interference light, associated with particle movement. A determination unit then evaluates peak levels of the detection signal before and after filtering to distinguish particle-origin signals from noise using a specific attenuation rate formula. If determined as particle-origin, a counting unit counts particles based on the filtered detection signal, else it suppresses false counts.
The problem addressed arises from noise sources like shot noise due to increased reference light intensity and spike noise due to electrical factors, which interfere with accurate particle detection and cause false counting. Conventional filtering alone is insufficient because noise may resemble particle signals with broad frequency components. The invention solves this by introducing a determination step based on attenuation rate in signal peak levels before and after filtering, effectively reducing false counts and enabling accurate particle counting per size.
Claims Coverage
The claims include one independent claim describing the main structure and functionalities of the particle counter and additional dependent claims refining threshold-based particle counting and filtering characteristics.
Particle counter with interference-based detection and filtering
A particle counter comprising a light source emitting light, a light superimposition unit to superimpose two branched lights, an irradiation optical system to irradiate fluid with one branched light forming a detection area, a detection optical system to make scattered light from particles enter the superimposition unit, a reference optical system to input another branched light as reference light, and a detector generating a detection signal of the interference light. The system includes a filter passing frequency components corresponding to variations in interference light intensity, a determination unit which compares peak levels of detection signals before and after filtering using an attenuation rate formula (Vp1 - Vp2)/Vp1 to decide if the signal arises from a particle, and a counting unit that counts particles based on filtered signal if determined as particle-origin.
Counting unit threshold setting dependent on attenuation rate
The counting unit performs particle counting based on comparing a count threshold value with the filtered detection signal and sets one of the attenuation rate threshold value or the count threshold value depending on the other, refining particle count accuracy.
Use of band-pass filter to isolate interference light frequency
The filter is specified as a band-pass filter that attenuates frequency components except those corresponding to intensity changes of the interference light caused by the particles, enhancing signal-to-noise ratio.
The claims cover a particle counter employing interference between scattered light and reference light combined with frequency filtering and a peak-level attenuation rate calculation to reliably distinguish particle signals from noise, enabling accurate particle counting.
Stated Advantages
Reduces false counting due to noise thereby improving accuracy in particle counting.
Enhances signal-to-noise ratio by filtering detection signals to pass frequency components corresponding to particle-induced intensity changes.
Allows accurate particle size discrimination and counting by utilizing peak level attenuation rate distinction between particle signals and noise.
Documented Applications
The particle counter is applied to measuring particles in fluids, including liquids such as chemical solutions and water, and gases such as air.
Specifically, the embodiments describe measuring particles in a liquid flow passage such as chemical solutions like isopropyl alcohol, hydrofluoric acid, and acetone.
Embodiments also indicate applicability to airborne particle counters.
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